Live Center / Dead Center?

Wreck™Wreck said:
Excellent learning experience here, If you want to get the best from a center live or dead, indicate the part at the chuck BEFORE drilling the center hole. Adjust the chuck by whatever means available be it an adjustable chuck mount, soft jaws or shims. If the center is not concentric with the chuck this will cause problems at the tail stock end, this often happens with cold rolled steel and aluminum round stock which is not terribly round as produced.

As an exercise put an indicator in the chuck, push the tail stock close enough to indicate it, put a dead center in the tail stock ram and spin the chucked indicator around it, a handheld mirror used to read the dial on the backside helps. Beware this may keep you up at nights if you are chasing tenth's at all times.
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What are "tenth's"? I see this mentioned on other threads but not being a machinist I'm not sure what that means.

I didn't get a chance to try the indicator in the chuck today so I might sleep tonight. :tranquility: I will give it try tomorrow, if time permits. We have all the family coming for a belated Christmas so I have a lot of preparations to get done before they arrive.

Last night I put a dead center in the tail stock and ran it up to a piece of material I turned to a point in the 3 jaw and discovered they did not line up horizontally. So I adjusted the tail stock to get them lined up. I also checked the run out on the 3 jaw, based on a piece of material I turned in it, and found the run out 1" from the jaws was nominal ( maybe 0.00025") hard to tell on my el cheapo indicator. At 6 " from the jaws there was a 0.002" variation between the lowest and highest reading. So I gather that means the run out is 0.001" at 6". Is that right? I'm not sure if I have already trued the backing plate and chuck for the 3 jaw or not. I know I did for the 4 jaw but I have spent so much time trying to make things right on this lathe that I forgot what I have already done. Might be time to make a list of the stuff I do from now on so I don't have to recheck. The 4 jaw had a terrible wobble in it and when checked there was a 0.012" face wobble and 0.010" OD wobble. I pulled the backing plate and it was bad too. So I trued that and now the 4 jaw is way better. I can't recall the results but I was happy with it. It still has the OD issue but I can't fix that since I don't have any cutters long enough to reach that far back.

This is my first lathe and I've a had a lot of issues with it. The lathe issues are listed in my intro and I have decided to just work my way through them rather than keep returning the machine to the dealer and waiting for replacements. Besides my 30 day return period is now up and I would have to pay to ship it to the service center for any warranty work. That would likely cost an arm, leg and other important body parts plus I would be without it for an extended time frame, each time it went back. I think I am getting close to resolving the major issues and then I can get down to learning how to run it rather than fix it. Sure can be frustrating at times but thanks to sites like this I can find the info I need to address the issues I've found so far.
 
HBilly1022 said:
What are "tenth's"? I see this mentioned on other threads but not being a machinist I'm not sure what that means.
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1/10,000th of an inch or, as stated above, 1/10th of 1/1,000th. In decimal format as such: 0.0001"

Us machinists have our own odd language. Especially when we pinch a body part. :mad:
 
This may be slightly off on a tangent, but turning between centers seems to have the best results for me when I want fairly tight tolerances. Of course you have to ensure that your centers are aligned.

If you haven't seen it yet, I'd recommend looking at "How To Run a Lathe" by South Bend. It you can download it for free here:

http://vintagemachinery.org/mfgindex/detail.aspx?id=1617&tab=3
 
I have live centers (LC), dead centers and dead centers with carbide tips. For the metal lathe operations I use the live centers. For the OD grinder operations, I use the dead centers. A good quality live center is not going to have any bearing play, it’s all under preload. For the HM, I see no problem in using a LC for metal lathe operations. And a helpful shop NOTE: if your work radically deviates from the datum center line when between centers. Then, I would recommend using a monobloc/conical center drill instead of a 60° center drill. It makes the marriage between the 60° point and the angled hole more conducive…Good Luck, Dave.
 
Charles Spencer said:
This may be slightly off on a tangent, but turning between centers seems to have the best results for me when I want fairly tight tolerances. Of course you have to ensure that your centers are aligned.

If you haven't seen it yet, I'd recommend looking at "How To Run a Lathe" by South Bend. It you can download it for free here:

http://vintagemachinery.org/mfgindex/detail.aspx?id=1617&tab=3
Click to expand...

Thanks for that link. I downloaded all the files and when I get some time I will turn my monitor sideways and start reading.

A tenth is 0.0001" ------- WOW that's small. I'm pretty sure the stuff I have turned so far has ridges in it way bigger than that. But with time, reading, help from here and practice I should get better.

I find it comical that I bought the lathe and a bandsaw at the same time, with the expectation that these will make my life easier. The bandsaw has done that, because I simply use it and the job gets done. The lathe however has turned into a whole new learning process which has occupied a LOT of my time since getting it. The more I use it, the more I find out that I need to learn . This could take over my life for a while. :)
 
No offense intended here but one thing I haven't seen clearly laid out yet is the fact that even the best 3-jaw chucks have a few thousandths of an inch of runout. Enough to make a visible "wobble" in the work if the work is not chucked up exactly in the same place as before.

From what I'm told, a 3-jaw chuck that is within .003" from the factory is considered excellent quality.
 
To elaborate on the "tenths" discussion.
Machinists work and talk in thousandths, so something like 1/2" is verbalized as "500 thousandths."
When working with 1/10,000 precision, we use the word "tenth."
Something like 0.0125" would be verbalized as "twelve thousandths and five tenths," which could be simply shortened to "twelve and five tenths." Alternatively it could be verbalized as "twelve and a half thousandths," or even less commonly "twelve point five thousandths."

When using the metric system, we always speak in millimeters. 0.02mm is simply "point zero two millimeters," or "two hundredths of a millimeter.

Many of us avoid the use of the word "mil" because it can cause confusion. Properly speaking in our field, a mil is 1/1000", but some metric people use the word mil as a short form of millimeter or millionth of a meter (0.001mm). This is actually a micrometer (it used to be called a micron). So if you come across diagrams or plans that use mils, they should be imperial measurements and interpreted as 0.001" not something metric.
 
Having worked through several issues on a G0602, which I really like, I would opine that your chucks may not be on a face plate which is perpendicular to the lathe axis of rotation. My three jaw was about 0.002 inches non-perpendicular at the edge of the face plate and the four jaw - way more. after a lot of measuring, some figuring and research, and getting trued, they are now OK. This improved my experience turning larger and longer items. A thinner bar, say 1/2 inch will bend enough to hit the center on the tail stock, while the 3 inch diameter bar, not so much. Maybe this will help locate the source of the problem. It is way too easy to try a bunch of things that don't solve the problem and actually cover up the real source. Until you get the workpiece in the chuck rotating on the axis of the lathe, you will have all sorts of problems. Also, If you got you center hot enough, that might also be a source of continued probl
 
HBilly1022 said:
What are "tenth's"?

Last night I put a dead center in the tail stock and ran it up to a piece of material I turned to a point in the 3 jaw and discovered they did not line up horizontally. So I adjusted the tail stock to get them lined up. I also checked the run out on the 3 jaw, based on a piece of material I turned in it, and found the run out 1" from the jaws was nominal ( maybe 0.00025") hard to tell on my el cheapo indicator.

.2500 = 250/1000"
.0250 = 25/1000"
.0025 = 25/10,000"
.00025 = 25/100,000"

If you indicated a part in place AFTER turning it this tells you nothing about the chuck itself as the lathe will make a very good circle about the axis of rotation of the spindle. If you scroll chucked a finished round, a gauge pin for instance, and it ran out .00025 then you are a lucky man indeed. A typical centerless grinder would be hard pressed to hold that size and circularity.

You almost certainly do not own the tools to measure such features accurately so don't sweat it, make parts that work for your particular application, chasing ever higher accuracy with a process such as turning in a lathe will result in making almost nothing to your satisfaction. By all means make the effort to do the best that you can but realize that a lathe of this type is not a machine that one would desire if holding tenths dimensions.

Good luck
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